To manufacture a thin disc such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices, about 3/4 mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the semiconductor wafer's surfaces. A similar polishing step is performed to planarize dielectric or metal films during subsequent device processing on the semiconductor wafer.
After polishing, be it during wafer or device processing, slurry residue conventionally is cleaned from wafer surfaces via submersion in a tank of sonically energized cleaning fluid, via spraying with sonically energized cleaning or rinsing fluid, or via a scrubbing device which employs polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes made from nylon bristles or similar materials. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless remain and produce defects during subsequent processing.
A conventional PVA brush scrubber disclosed in U.S. Pat. No. 5,675,856 is shown in the side elevational view of FIG. 1. The conventional scrubber 11, own in FIG. 1, comprises a pair of PVA brushes 13a, 13b. Each brush comprises a plurality of raised nodules 15 across the surface thereof, and a plurality of valleys 17 located among the nodules 15. The scrubber 11 also comprises a platform 19 for supporting a wafer W and a mechanism (not shown) for rotating the pair of PVA brushes 13a, 13b. The platform 19 comprises a plurality of spinning mechanisms 19a-c for spinning the wafer W. During scrubbing a fluid supply mechanism F, such as a plurality of spray nozzles, supplies fluid to both major surfaces of the wafer, flushing dislodged particles and cleaning residue from the major surface of the wafer and rinsing brushes.
Preferably, the pair of PVA brushes 13a, 13b are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer's edges. However, research shows that slurry induced defects still occur, and are caused by slurry residue remaining along the edges of the wafer despite cleaning with apparatuses such as that described above. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects. The same is believed to be true of all major surface cleaners, and scrubbers.
For instance, another conventional technique for cleaning slurry residue and other particles from the surfaces of a semiconductor wafer employs sonic nozzles that direct jets of liquid toward a major surface of a semiconductor wafer. FIG. 2 is a side elevational view of an exemplary sonic nozzle cleaning device 23 that includes a sonic nozzle 25 having an input port 25a, an output port 25b, and a vibrator 27 coupled to a generator 29 that drives the vibrator 27.
In operation, a cleaning solution (e.g., de-ionized water or another similar cleaning solution such as NH.sub.4 OH, KOH, TMAH, HF, citric acid or a surfactant) is supplied under pressure (e.g., 15 p.s.i.) to the input port 25a of the nozzle 25. The cleaning solution travels through the nozzle 25, passes under the vibrator 27 and travels through the output port 25b. As the cleaning solution leaves the output port 25b it strikes the major surface of an object to be cleaned (e.g., a major surface 31a of a semiconductor wafer 31).
The vibrator 27 vibrates at a sonic rate (e.g., ultrasonic at a frequency in the hundreds of kHz or megasonic at a frequency in the thousands of kHz) set by the generator 29. As the cleaning solution travels under the vibrator 27, the vibrator 27 induces longitudinal pressure waves 33 in the cleaning solution. The longitudinal pressure waves 33 travel to, strike and impart energy to the major surface 31a of the semiconductor wafer 31 approximately every 0.1 to 10 microseconds, depending on the particular frequency of the generator 29, thereby removing slurry residue and other particles from the major surface 31a of the wafer 31. The entire major surface 31a of the wafer 31 is cleaned by scanning the nozzle 25 across the wafer 31 while rotating the wafer 31 with a rotating mechanism 34. Slurry residue and other particles on the edges of the wafer 31, however, are not effectively cleaned by the jets of cleaning solution employed by this type of cleaning apparatus.
A number of devices have been developed to improve wafer edge cleaning. One such device is shown in the side elevational view of FIG. 3. This mechanism employs a separate edge brush 21, which is driven by a separate motor (not shown), that causes the edge brush 21 to rotate. The edge brush 21 fits over the edge of the wafer W as shown in FIG. 3, providing more effective wafer edge cleaning. Although the edge brush 21 addresses the need to clean slurry residue from wafer edges, it does so at the expense of increased scrubber complexity and cost, and the requirement of frequent edge brush replacement because of excessive mechanical wear.
Accordingly the field of wafer cleaning requires a method and apparatus which effectively cleans both the major surfaces and the edge surfaces of a semiconductor wafer, and that does so without increased cost and complexity. In short, the semiconductor processing field needs an effective edge cleaner that satisfies the ever-present demand for reduced cost per unit wafer processed.